Internet Protocol Television (IPTV) is a video service offered by a service provider that controls the network infrastructure and content distribution to its customers. Usually, IPTV services run over a multiservice IP infrastructure, which provides data, voice and video on the same infrastructure.
IPTV is seen as a technology having huge business potential. However, to be able to distribute high quality digital content over “open” technology such as IP calls for strong protection of the interests of content owners so that they can be guaranteed a reasonable payment for their supplied content and do not end up handing out content “for free” owing to unauthorised copying, etc. This has lead to the development of systems of Digital Rights Management (DRM) that are intended to restrict in some way how supplied content may be used. However, users are generally not very fond of DRM and thus a solution that is secure from content owners point of view, as well as being convenient and “fair” from users' point of view is essential.
Traditionally, DRM has been tied to the specific device receiving the content and it has been difficult to allow sharing of content across devices. However, users are accustomed to share content across devices, from the time content distribution was made by physical means such as CDs and tapes. Therefore, a need has been identified for a DRM concept based on domains wherein content can be shared.
In general, a DRM system would satisfy all or most of the following requirements:                Content must be packaged for protection during transmission or storage; this is usually accomplished by encryption.        It must be possible for users to freely store or backup protected content (usually encrypted as explained above). However, the system must prevent unauthorized content usage, in accordance with purchase terms between the content owner and the user, which terms may, for example, forbid free distribution of the content.        The system must be independent of media transport mechanism (i.e. UDP, RTP, etc.), distribution service (i.e. broadcast, video-on-demand, etc.), and it must support any kind of content (i.e. audio, video).        The distribution of content to users should be independent of distribution of the content's license/key to the user. It should be possible to manage contents and licenses separately in the client application.        DRM control on the end-to-end media distribution must be possible.        The system must be independent of platform and device type.        
Examples of DRM systems have been proposed by the Open Mobile Alliance (OMA) in “OMA DRM Architecture, Approved version 2.0”, March, 2006 and by the Marlin project in “Marlin Architecture Overview”. OMA and Marlin are generic DRM solutions.
The Marlin and OMA DRM systems are based on domains, which allow content sharing between devices and/or users within the domain. This feature is very important for IPTV environment where the content must be shared between family members/devices and, possibly, temporary guests. The domain concept is slightly different for each system, as is the Service Distribution Provider (SDP) control on the formation of the domain. This feature could limit either the possible fair usage of the content or the user privacy, as discussed below. Another aspect is how the SDP controls the content sharing inside the domains and between domains. This is necessary for copyright control by the SDP, regarding the security policy in the corresponding license.
In OMA, licenses are issued for domains, and distributed to devices through a domain shared key. Then, any device in the domain is authorized to use the content supplied under a license to a domain. The SDP is the domain manager in OMA. The user must request device registration in the domain for content usage. This allows the SDP to control the maximum number and types of devices in a domain. On the other hand, the SDP then knows about the user devices, the specific content used and, depending on the IPTV solution used, the private user data, thus potentially violating user privacy.
Thus, in OMA, domain management is not under the control of the user which could be an obstacle for widespread user acceptance, e.g. inflexibility and inconvenience as well as possible loss of user privacy may be an issue. For example, buying a new device and making it part of the “home” domain may be a complicated operation and a user may not want to tell the SDP which devices he has in his possession.
Marlin DRM is more flexible, and it seems to satisfy basic IPTV scenarios.
The domain can in some use-cases be managed by users, thus avoiding violation of user privacy. Any device in the domain can use the content. However, Marlin is also more complex than OMA. The SDP controls the content sharing through the domain policy in the license, which is issued for users. The domain policy can limit the number of domains with which a user can be associated, and can limit the number of devices by domain. Therefore, the SDP control on media sharing can constrain the user freedom for content usage in the intended IPTV scenarios. For example, a license may contain the policy “this content can only be played if the owner is associated to a maximum of X domains; and the domain, which the license is shared for, has a maximum of Y devices.”.
Marlin gives the user more control, but the service provider still has strong control on domain formation, when it defines, in the license, the maximum number of devices that a domain may have. This implies a restriction in users' freedom.